The present invention relates to a refrigerator having a defrosting device for defrosting an evaporator with a heater.
In recent years, art associated with a freezing refrigerator having a defrosting device for an evaporator is disclosed in Japanese Unexamined Patent Publication No. HEI 8-54172. A schematic side sectional view showing a structure thereof is shown in FIG. 31. Hereinafter, a conventional freezing refrigerator will be explained by referring to the drawings.
In FIG. 31, reference numeral 1 denotes a refrigerator housing. Reference numeral 2 denotes a freezing chamber located inside the refrigerator housing 1. Reference numeral 3 denotes a refrigerator chamber located inside the refrigerator housing 1. Reference numeral 4 denotes a door of the freezing chamber. Reference numeral 5 denotes a door of the refrigerator chamber. Reference numeral 6 denotes a partition wall for partitioning the freezing chamber 2 and the refrigerator chamber 3 from each other. Reference numeral 7 denotes an inlet port of the freezing chamber 2 for sucking air into the freezing chamber. Reference numeral 8 denotes an inlet port of the refrigerator chamber 3 for sucking air into the refrigerator chamber. Reference numeral 9 denotes a discharge port for discharging cool air. Reference numeral 10 denotes an evaporator. Reference numeral 11 denotes a fan for circulating cool air.
Reference numeral 12 denotes a partition wall of the evaporator 10 for partitioning the evaporator and the freezing chamber 2. Reference numeral 13 denotes a basin. Reference numeral 14 denotes a drain outlet. Reference numeral 15 denotes a defrosting tube heater in which a Nichrome wire held in a coil-like configuration is covered with a glass tube. Reference numeral 16 denotes a roof for preventing an evaporation sound, generated when a defrost water is directly dripped on the defrosting tube heater 15. Reference numeral 17 denotes a metal-made bottom surface plate mounted between the basin 13 and the defrosting tube heater 15 to be insulated and held.
In this conventional refrigerator, when the freezing chamber 2 and the refrigerator chamber 3 are cooled, coolant is allowed to flow through the evaporator 10 so that the evaporator 10 is cooled. In the same manner, with operation of the fan 11, air having an increased temperature in the freezing chamber 2 and the refrigerator chamber 3 is sent to a cooling chamber, and this air is cooled via heat exchange in the evaporator 10. Then, the cooled air is sent to an interior of the freezing chamber 2 from the discharge port 9 so that cold air is sent to the refrigerator chamber 3 through a communication port (not shown) from the freezing chamber 2.
Generally, air which has undergone heat exchange within the evaporator 10 is highly humidified with an inflow of high temperature outside air as a result of frequent opening and closing of door 4 and door 5, and evaporation of moisture content of conserved food in the freezing chamber 2 and the refrigerator chamber 3, or the like, so that moisture in the air becomes frosted and adheres to the evaporator 10, which has a temperature lower than the air. With an increase in frost quantity, heat transmission with air undergoing heat exchange with a surface of the evaporator 10 is hindered, while a heat passage ratio is lowered because of lowering of conveyed air quantity resulting from ventilation resistance, with a result that a cooling shortage is generated.
Therefore, before a frost quantity becomes superfluous, the Nichrome wire of the defrosting tube heater 15 is electrified. When electrification of the Nichrome wire is started, heat is radiated to the evaporator 10 and peripheral parts from the Nichrome wire. At this time, heat radiated to the bottom plate 17 is partially reflected according to a form of the bottom plate 17, while remaining heat is reflected toward the evaporator 10 and the peripheral parts. As a consequence, frost which adheres to and near the evaporator 10, the basin 13 and the exhaust port 14 is melted into water. Additionally, in this manner, a portion of defrosted water which is melted in this manner is directly dripped on the basin 13 while a remaining portion makes a detour of the defrosting tube heater 15 to fall to the basin 13 by way of the roof 16, to be exhausted to an exterior from the drain outlet 14.
However, with the above structure, when the defrosting tube heater 15 is generally electrified, not only a surface temperature of the Nichrome wire, but also a surface temperature of the glass surrounding the wire, come to have a high temperature. At the same time, since the bottom plate 17 is located in the vicinity of the tube heater 15, part of heat radiated from the tube heater 15 is reflected again to the tube heater 15 with a result that a heated temperature of the tube heater 15 unusually rises and attains a value not lower than an ignition temperature of a flammable coolant to be used. Accordingly, there is a problem in that in a case where the flammable coolant is used as a coolant, leakage of the flammable coolant from piping mounted on a portion communicating with the evaporator 10 and inside of the refrigerator leads to danger of ignition of the flammable coolant with electrification of the defrosting heater 15, so as to result in an explosion.
In view of the above problem, an object of the present invention is to provide a freezing refrigerator which can suppress danger of ignition of a flammable coolant even in a case where defrosting is conducted in an environment in which the flammable coolant is leaked to an atmosphere of a defrosting device.
In order to attain the above object, the refrigerator according to the present invention comprises a freezing cycle for connecting a compressor, a condenser, a depression mechanism and a vaporizer to seal flammable coolant, and a defrosting heater or device for defrosting the vaporizer, wherein a heated temperature of the defrosting heater during operation becomes only lower than an ignition temperature of the flammable coolant. Consequently, when the flammable coolant is leaked to an inside of the refrigerator because of breakage of piping or the like, danger of ignition is extremely lowered even when heating of the defrosting heater or device is started.
As the defrosting device, it is desirable to mount a glass tube and a heater wire formed of metal resistor inside of the glass tube. In such a case, it is desirable to heat the heater wire up to a temperature lower than the ignition temperature of the flammable coolant. Since a majority of heat resulting from the heater wire, which is a heating body, is radiated to frost which has adhered to the evaporator and peripheral parts, defrosting is conducted during a defrosting time which is the same as, or less than conventional defrosting time, while corrosion and deterioration or the like resulting from direct contact with exterior air can be prevented. Consequently, while a defrosting capability and life of the defrosting device that is the same as, or more than, conventional defrosting capability and life can be secured, a surface temperature of the heater wire which is likely to come into contact with exterior air can be set to a level that is the same as, or lower than, the ignition temperature of the flammable coolant.
It is desirable that a surface at a central portion of a length of a spiral portion of the heater wire has a heated temperature lower than the ignition temperature of the flammable coolant. By doing so, it is possible to set a surface temperature of the heater wire at the central portion, which has a high temperature, to a temperature that is the same as or lower than the ignition temperature of the flammable coolant in a length direction of the spiral portion, while securing a defrosting capability and life to be the same as, or more than, conventional defrosting capability and life. Consequently, a temperature of the heater wire in its entirety can be set to lower than the ignition temperature of the flammable coolant.
As another method, it is desirable to heat a heaterwire so that a surface temperature of a spiral portion thereof is set to a temperature lower than an ignition temperature of a flammable coolant to be used. By so doing, while securing a defrosting capability and life to be the same as, or more than, conventional defrosting capability and life, it is possible to set, to a temperature lower than the ignition temperature of the flammable coolant, a heated temperature at an upper portion of the heater wire which comes to have a higher temperature above and below the spiral portion because of movement of high temperature gas resulting from heating of the heater wire. Consequently, it is possible to allow the heater wire in its entirety to have a temperature lower than the ignition temperature of the flammable coolant.
Preferably, the above heater wire comprises a straight portion formed in a straight configuration at both ends thereof, and a spiral portion formed in a spiral configuration at another portion between both ends. It is desirable that a heating value per unit area becomes lower than 2.5 W/cm2, which quantity is obtained by dividing a heating value resulting from Joule heat of the spiral portion by a surface area thereof. Consequently, it is possible to secure a defrosting capability and life to be the same as, or more than, conventional defrosting capability and life. Furthermore, the heater wire comes to have a temperature lower than the ignition temperature of the flammable coolant by setting to lower than 2.5 W/cm2 the heating value per unit area of the spiral portion which comes to have a higher temperature under influence from mutually adjacent portions of the heater wire, as compared with the straight portions of the heater wire.
Furthermore, when an entire heating value of the heater wire is increased, a surface temperature of the heater wire rises. However when the heater wire is designed in such a manner than the heating value per unit area is lower than 2.5 W/cm2, even when the entire heating value is increased, a temperature of the heater wire can be lower than the ignition temperature of the flammable coolant irrespective of the heating value of the heater wire in its entirety.
Accordingly, design of a defrosting device can be easy, which enables setting a temperature of a heater wire to a value lower than an ignition temperature of a flammable coolant to be used, while maintaining a temperature of the heater wire lower than the ignition temperature of the flammable coolant.
Furthermore, the heater wire may have a value of lower than 8.5 W/cm3, which value is obtained by dividing a heating value of the spiral portion by a volume surrounded by an outer diameter and length of the spiral portion. In this case as well, a defrosting capability and life that are the same as, or more than, conventional defrosting capability and life can be secured while a temperature of the heater wire can be increased while maintaining this temperature to be lower than an ignition temperature of a flammable coolant to be used.
Furthermore, in a case where the outer diameter of the spiral portion changes, a temperature of the heater wire becomes lower than an ignition temperature of a flammable coolant to be used without affecting the outer diameter of the spiral portion of the heater wire when the spiral portion is designed so that a heating value with respect to volume calculated from the outer diameter and length of the spiral portion becomes lower than 8.5 W/cm2.
As another method, it is desirable to set to lower than 9.2 W/cm2 a value obtained by dividing a heating value of the spiral portion of the heater wire by a surface area thereof. As a consequence, it is possible to secure a defrosting capability and life to be the same as, or more than, conventional defrosting capability and life while an entire heating value of the heater wire can be increased while maintaining a temperature of the heaterwireto be lower than an ignition temperature of a flammable coolant to be used.
Furthermore, in a case where pitch and outer diameter of the spiral portion has changed as well, a temperature of the flammable coolant becomes lower than the ignition temperature of the flammable coolant without affecting the change in the pitch and outer diameter of the spiral portion by designing the spiral portion in such a manner that a value becomes lower than 9.2 W/cm2, which value is obtained by subtracting a heating value per unit area of the spiral portion from a coefficient obtained by dividing the pitch of the spiral portion by the outer diameter of the spiral portion.
Furthermore, when pitch of the spiral portion of the heater wire is 2 mm or more, influence on the heater wire from mutually adjacent portions of the spiral portion of the heater wire can be decreased. Accordingly, since temperature unevenness resulting from unevenness of pitch of the spiral portion can be decreased, a temperature of the heater wire in its entirety becomes lower than an ignition temperature of a flammable coolant to be used.
Additionally, when the heater wire is partially formed of a metal which is melted and disconnected at a temperature lower than an ignition temperature of a flammable coolant to be used, a temperature of the heater wire is transmitted to metal of a temperature fuse when a heated temperature of the heater wire comes close to the ignition temperature of the flammable coolant. As a consequence, at a predetermined temperature lower than the ignition temperature of the flammable coolant, metal of the temperature fuse is melted and disconnected so that a rise in temperature of the heater wire to, or greater than, the ignition temperature of the flammable coolant is suppressed by shielding of input.
Furthermore, according to a preferred embodiment of the present invention, a temperature fuse formed of metal which is melted and disconnected at a temperature lower than an ignition temperature of a flammable coolant to be used is connected in series to a defrosting device, and the temperature fuse is located in the vicinity of the defrosting device. Thus, when temperature of a heater wire comes close to the ignition temperature of the flammable coolant, a heated temperature of the heater wire is transmitted to the temperature fuse with a result that the metal of the temperature fuse is melted at a predetermined temperature lower than the ignition temperature of the flammable coolant, and a rise in temperature of the heater wire to a temperature not lower than the ignition temperature is suppressed with shielding of input. Furthermore, in a case where the temperature fuse is damaged under some influence, and no problem is caused in the defrosting device, only the temperature fuse is replaced. Thus, maintenance is easy.
Incidentally, the temperature fuse may be mounted in close contact with a defrosting device, or the temperature fuse may be allowed to adhere to a hull surface of an upper portion of a defrosting device. In the former example, there is provided an effect such that a surface temperature of the defrosting device is accurately transmitted to the defrosting device, and a rise in temperature of the defrosting device to a temperature not lower than an ignition temperature of a flammable coolant to be used can be suppressed while maintenance only of the temperature fuse is easy. In the latter example, there is provided an effect such that when a temperature of the upper portion of the defrosting device, which is a high temperature portion in a vertical direction, is detected the temperature fuse is melted and disconnected, and a rise in temperature of the defrosting device in its entirety to a temperature not lower than the ignition temperature of the flammable coolant can be suppressed by shielding of input at a predetermined temperature lower than the ignition temperature of the flammable coolant while maintenance is easy.
A temperature fuse formed of a metal which is wired in series with a defrosting device and which is melted and disconnected at a temperature lower than an ignition temperature of a flammable coolant to be used may be allowed to adhere to a surface of a hull of a lower portion of the defrosting device, or a surface of a hull of a central portion in a length direction of the defrosting device. In the former case, there is provided an effect such that a temperature of the temperature fuse is not lowered because of a direct contact with defrost water which is dripped from an evaporator or the like located at an upper portion of the defrosting deivce, so that a heated temperature of the defrosting device can be accurately detected, and a rise in temperature to at least the ignition temperature can be more accurately suppressed while maintenance is easy. In the latter case, there is provided an effect such that when a temperature of the central portion, which is a high temperature portion, in the length direction of the defrosting device becomes a temperature lower than the ignition temperature of the flammable coolant, the temperature fuse which is mounted in close contact with the portion is melted and disconnected, and a rise in temperature of the defrosting device is further suppressed to no more than the ignition temperature with shielding of input while maintenance of only the temperature fuse is easy.
According to a preferred embodiment of the present invention, a defrosting device comprises a glass tube and a heater wire formed of a metal resistor inside of the glass tube. A temperature fuse is mounted on the glass tube in close contact therewith, so that metal which forms a constituent element of the temperature fuse is melted and disconnected at a temperature which is lowered by 100 to 200xc2x0 C. from an ignition temperature of a flammable coolant to be used. Consequently, when the heater wire, which is a heating body, attains a temperature in the vicinity of the ignition temperature of the flammable coolant, and a predetermined temperature lower than the ignition temperature, a surface of the glass tube on an outer periphery of the heater wire comes to have a temperature 100 to 200xc2x0 C. lower than the predetermined temperature with heat lost when transmitted from the heater wire to the glass tube. Accordingly, the temperature fuse mounted in close contact with the surface of the glass tube is melted and disconnected, and a rise in temperature to a value the same as or more than the ignition temperature of the flammable coolant with shielding of input is further suppressed while maintenance of only the temperature fuse is easy.
As another method, a heater wire comprises a straight portion formed in a straight configuration and a spiral portion formed in a spiral configuration. A temperature fuse may be formed of metal which is melted and disconnected at a temperature lower than an ignition temperature of a flammable coolant to be used, and may be mounted on a surface of a glass tube on an outer periphery of the straight portion of the heater wire. In such a case, when the heater wire comes to have a predetermined temperature lower than the flammable coolant, the temperature fuse which is mounted on the surface of the glass tube in close contact therewith is melted and disconnected, and a rise in temperature of a defrosting device to a temperature not lower than the ignition temperature of the flammable coolant is suppressed by shielding of input while maintenance only of the temperature fuse is easy. Furthermore, since a glass surface temperature on the outer periphery of the straight portion is low with respect to a surface of the glass tube on an outer periphery of the spiral portion of the heater wire, a temperature fuse which is melted and disconnected at a low temperature can be used and cost thereof is low.
Furthermore, as another method, a defrosting device comprises a glass tube and a heater wire formed of a metal resistor mounted on the glass tube. The heater wire comprises a straight portion at both ends thereof, and a spiral portion. Preferably, a temperature detection device is provided on a glass surface on an outer periphery of one of the straight portions of the heater wire. In this case, when the temperature detection device detects a temperature not lower than a predetermined temperature, input of the heater wire is shielded with a result that a rise in temperature to a value not lower than an ignition temperature of a flammable coolant to be used is further suppressed by the shielding of the input. Furthermore, since a glass temperature on an outer periphery of the straight portions is low with respect to a surface of the glass tube on an outer periphery of the spiral portion of the heater wire, a temperature detection deivce for detection at a low temperature can be used and cost thereof is low.
It is desirable that the temperature detection device conducts a shut-off operation at a temperature which is 310 to 410xc2x0 C. lower than the ignition temperature of the flammable coolant. In such a case, when temperature of the heater wire rises to a temperature in the vicinity of the ignition temperature of the flammable coolant, the temperature detection device detects a temperature which is 310 to 410xc2x0 C. lower than the ignition temperature of the flammable coolant to shield input of the defrosting device. Accordingly, a rise in temperature of the heaterwire to a value not lower than the ignition temperature of the flammable coolant can be further suppressed, and furthermore, a relatively cheap temperature detection device can be used and cost thereof is low.
In a case where the defrosting device comprises a glass tube and a heater wire formed of a metal resistor inside the glass tube, and the heater wire is formed of a straight portion at both ends thereof, and a spiral portion formed in a spiral configuration at a remaining portion between both ends, heating value per unit area obtained by dividing a heating value resulting from Joule heat of the spiral portion by a surface area of an inner surface of the glass tube is desirably less than a predetermined quantity. With this structure, a surface temperature of the glass tube can be lowered and a surface temperature of the heater wire can be lowered while securing an entire quantity of heat radiated to an exterior through the glass tube from the heater wire. Furthermore, there is also provided an effect such that a defrosting capability and life that are not lower than a conventional defrosting capability and life can be secured while lowering a surface temperature of the heater wire.
As another method, when a heating value per unit area, obtained by dividing a heating value resulting from Joule heat of a spiral portion of a heater wire by a surface area of an inner surface of a glass tube, is set to lower than 1.6 W/cm2, Joule heat from the heater wire is radiated to an exterior smoothly through the glass tube, so that a surface temperature of the heater wire is lowered. While a defrosting capability and life that are not lower than a conventional defrosting capability and life can be secured, a surface temperature of the heater wire can be lower than an ignition temperature of a flammable coolant to be used. Furthermore, when Joule heat of the heater wire to be used is known, a temperature of the heater wire can be lower than the ignition temperature of the flammable coolant while securing a defrosting capability and life that are not lower than a conventional defrosting capability and life only by determining an inner diameter of the glass tube so that the heating value per unit area of the inner surface of the glass tube becomes lower than 1.6 W/cm2. Thus, design is easy.
Incidentally, preferably, a clearance between the inner surface of the glass tube and the heater wire is 1 mm or less. As a consequence, hindrance of heat transmission with gas present between the glass tube and the heater wire can be decreased, and heat radiated from the heater wire is radiated to the exterior through the glass tube. Furthermore, a quantity of heat radiated to the exterior increases and a defrosting capability is improved while a quantity of heat used in a rise of a heated temperature of the heater wire decreases for the increased portion of the quantity of heat radiated to the exterior with a result that a surface temperature of the heater wire is lowered to a value lower than the ignition temperature of the flammable coolant.
The inner surface of the glass tube and the heater wire may come into contact with each other. In this case, hindrance of heat transmission by gas between the glass tube and the heater wire is removed, so that heat radiated from the heater wire is smoothly radiated to the exterior. Accordingly, a quantity of heat radiated to the exterior further increases and a defrosting capability is further improved while a quantity of heat used in a rise in a heated temperature of the heater wire decreases for an increased portion of the quantity of heat radiated to the exterior. Consequently, a surface temperature of the heater wire is further lowered and can be lower than the ignition temperature of the flammable coolant.
As another method, a roof located above a glass tube is provided, and a minimum distance between an outer surface of the glass tube and the roof may be chosen to be a predetermined value. In this case, the roof decreases a hindrance of gas convection in the vicinity of the glass tube, and heat radiation by convection from the glass tube is improved while heat radiation of a heater wire, which is a heat receiving source of the glass tube, is also improved. Thus, a surface temperature of the heater wire is lowered to a value lower than an ignition temperature of a flammable coolant to be used.
Furthermore, it is desirable that a thickness of the glass tube is 1.5 mm or less. Consequently, heat transmission quantity at a time of transmitting heat, than an inner surface of the glass tube receives from the heater wire, to an outer surface of the glass tube increases so that heat discharged from the heater wire is radiated to the exterior through the glass tube. Accordingly, a quantity of heat radiated to the exterior increases, and a defrosting capability is further improved while a quantity of heat used for a rise in a heated temperature of the heater wire decreases for an increased portion of the quantity of heat radiated to the exterior. Consequently, a surface temperature of the heater wire is further lowered to be lower than the ignition temperature of the flammable coolant.
Alternatively, when the glass tube is made of quartz glass, breakage resulting from a linear swelling difference at a time of temperature change of the glass tube resulting from heating of the heater wire can be prevented, and a direct contact of the leaked flammable coolant with the heater wire can be prevented in a case of leakage of the flammable coolant to an atmosphere of the defrosting device.
A freezing refrigerator according to one preferred embodiment comprises: a refrigerator housing in which a freezing chamber and a refrigerator chamber are completely independent; a cooling system for functionally connecting a compressor, a condenser, a refrigerator chamber cooling device which has a high evaporation temperature for refrigeration, a depression mechanism for a high evaporation temperature having a small depression for a high evaporation temperature, a freezing chamber cooling device having a low evaporation temperature for freezing, which device is connected in parallel with the refrigerator chamber cooling device, a depression mechanism for low evaporation temperature having a large depression for a low evaporation temperature, a change-over valve for controlling that no coolant flows simultaneously to the refrigerator chamber cooling device and the freezing chamber cooling device, and a check valve for preventing a reverse current of the coolant to an outlet of the freezing chamber cooling device to seal a flammable coolant; and a defrosting device for defrosting the freezing chamber cooling device. Since the defrosting device defrosts at a temperature lower than an ignition temperature of the flammable coolant, a frost quantity in the freezing chamber cooling device is decreased because of the fact that all chambers, including the freezing chamber and the refrigerator chamber, are cooled with one cooling device in the prior art while only the freezing chamber is cooled in the freezing refrigerator of the present invention. For completing defrosting in the same amount of defrosting time as in the prior art, a defrosting device with defrosting capability which requires a smaller heating value can be used.
Consequently, an attempt can be made to lower a temperature during use of the defrosting device with a lower heating value. The defrosting device can defrost at a temperature lower than an ignition temperature of the flammable coolant, and energy can be saved.
Preferably, the defrosting device comprises a glass tube and a heater wire formed of a metal resistor inside the glass tube. A roof comprises inclined plates which are inclined in directions opposite to each other. Since respective inclined plates partition each other in a vertical direction, peripheral air which is heated with the defrosting device and rises by convection passes through a central slit of the roof formed between the inclined plates into an above evaporator, so that heat radiation by the defrosting device is promoted. Accordingly, a quantity of heat radiated to an exterior further increases and a defrosting capability is further improved, while for the increased portion of the quantity of heat radiated to the exterior the quantity of heat used in a rise in a heated temperature of the heater wire decreases, so that a surface temperature of the heater wire is further lowered to be lower than an ignition temperature of a flammable coolant to be used.